The 30-30 Rule for Lightning Safety (NWS Guidance)

The 30-30 rule is a simple lightning-safety guideline taught by the National Weather Service. It has two parts, and both numbers are 30 for a reason.

The first 30: if you see lightning and hear thunder within 30 seconds, the storm is close enough to be dangerous — about six miles or less — and you should already be in a safe shelter. The second 30: wait at least 30 minutes after the last clap of thunder before heading back outside.

Those final 30 minutes catch the strikes people most often underestimate. A storm that appears to have passed can still send a bolt several miles ahead of or behind itself, into skies that look clear.

Most lightning casualties happen at the edges of a storm — as it approaches before the rain, and as it departs while the sky brightens. People head back to the field, the trail, or the pool too soon.

The 30-minute wait is the part of the rule most often skipped, and it is the part that prevents the most injuries. Reset the clock every time you hear thunder; the count starts again from the last rumble, not the first.

A safe shelter is a substantial, enclosed building with wiring and plumbing, or a fully enclosed metal-topped vehicle with the windows up. Picnic shelters, dugouts, tents, and open garages do not count.

There is no safe place outdoors during a thunderstorm. The NWS slogan is blunt and worth remembering: when thunder roars, go indoors.

The 30-30 rule works on the storm you can already hear. A tracker gives you the part the rule cannot: a warning before the first close strike, and confirmation that the storm has truly moved on.

StrikeCast shows the distance in miles to the nearest strike and whether it is approaching, drawn from NOAA GOES-GLM satellite data. Save the places you care about and the app pushes a free alert when lightning closes in — so you can start your shelter timer early and stay safe through the trailing 30 minutes.